Salinity difference between devices

[Reef.]

Can’t see what I’m doing wrong.

Tested my salinity with a TM hydrometer, result 1.0285, temp 78, which is around 38ppt test the same display water with two ATC refractometers, both read 35ppt, checked the refractometers with salinity reference solution.

Why am I getting too different results from the same water?

 

[Lavey29]

Did you have all flow off with the hydrometer?

 

[JNalley]

Use a graduated cylinder, put the hydrometer in the cylinder with water, read from the bottom of the meniscus not the water line. Same result?

 

[Reef.]

Did you have all flow off with the hydrometer?

I use a measuring cylinder, previously checked the hydrometer with Randy’s reference solution.

 

[Reef.]

Use a graduated cylinder, put the hydrometer in the cylinder with water, read from the bottom of the meniscus not the water line. Same result?

Yes, same result, can’t be a temp issue as the hydrometer is calibrated to 77 and the tank water is 78 so not even worth correcting for temp.

 

[JNalley]

Yes, same result, can’t be a temp issue as the hydrometer is calibrated to 77 and the tank water is 78 so not even worth correcting for temp.

Then I am not sure why the disparity... Properly calibrate refractometers are supposed to be more accurate though...

 

[Reef.]

Then I am not sure why the disparity... Properly calibrate refractometers are supposed to be more accurate though...

More accurate than a floating hydrometer?

 

[JNalley]

More accurate than a floating hydrometer?

Yes, at least according to industry experts in industries that use both (Brewing, juicing, reefing, oil, etc.)

 

[Reef.]

Solved it, was doing my head in…I wasn’t waiting long enough for the ATC on the refractometer to kick in fully, I would see the 35ppt reading and not bother to wait to see if the reading was still changing.

Never really read of a recommended wait time for the ATC to do it’s thing, how long does everyone wait?

 

[EricR]

Refractometers aren't my thing but I do use Randy's formulas for EC (Hanna) calibration and spot check of hydrometers -- different ratios so hopefully you got that.

Beyond that, I think I trust TM precision hydrometer (in no flow 500mL cylinder, like you mentioned) the most.

...but then there's always the question of how much do you trust your temperature measurement?
*almost kidding on that since, within reason, it doesn't make a huge difference, but still

 

[TangerineSpeedo]

Yes, at least according to industry experts in industries that use both (Brewing, juicing, reefing, oil, etc.)

? Hmm. Could you cite some of those experts? NOT saying your wrong, just that is the opposite of what I have learned. A floating hydrometer is a lab created standard that is calibrated to read consistently at predetermined temperature. Whereas a refractometer can be greatly affected by ambient air temperatures. It is easier to control the consistency of the temperature of the fluid surrounding a floating hydrometer than the ambient temperature of a reflectometer.

 

[Reef.]

Refractometers aren't my thing but I do use Randy's formulas for EC (Hanna) calibration and spot check of hydrometers -- different ratios so hopefully you got that.

Beyond that, I think I trust TM precision hydrometer (in no flow 500mL cylinder, like you mentioned) the most.

...but then there's always the question of how much do you trust your temperature measurement?
*almost kidding on that since, within reason, it doesn't make a huge difference, but still

Been down that rabbit hole, as you say temp doesnt alter the result significantly within a degree or so but my thermometer is calibrated to within 0.1c so I’m happy my temp is correct.

This has given me a knew appreciation for the hydrometer and surprisingly also the refractometer.

 

[JNalley]

? Hmm. Could you cite some of those experts? NOT saying your wrong, just that is the opposite of what I have learned. A floating hydrometer is a lab created standard that is calibrated to read consistently at predetermined temperature. Whereas a refractometer can be greatly affected by ambient air temperatures. It is easier to control the consistency of the temperature of the fluid surrounding a floating hydrometer than the ambient temperature of a reflectometer.

To be clear here, most refractometers these days are ATC (Auto Temperature Compensation) Refractometers, refractometers were also initially created in a lab, and the ATC kind have a typical variability of 10-30 C (Meaning that you won't get inaccuracy until the ambient temperature is below 10C or above 30C (50 F - 86 F). They, too, are often created/calibrated at a specific ambient temperature (in this case, 20C or 68F is most often chosen as the normal/calibrated ambient room temperature).

From my understanding of the articles I've read, which mainly cover in-the-field usage, it weighs out like this:

Cons that lead to inaccuracy:
Hydrometer Cons:
-Affected by micro-bubbles
-Affected by microscopic solids in the solution you're measuring (not dissolved solids (This was in an article about using them to measure sugar concentration in juice from fruits or grapes (winemaking). I am not sure how relevant it is to our hobby, though a copepod or film algae clinging to the outside is certainly analogous to what the article was saying)
-Affected by the temperature of the solution in the cylinder (most of them stated circumvention involves measuring the temperature until it reaches an equilibrium with the ambient temp and then recording both the temperature and the reading and then performing math to get the correct reading)
-Highly Fragile (something about the card in the stem showing the readings, I didn't fully understand it)
-Susceptible to any residue from improper cleaning in both the cylinder and on the hydrometer

ATC Refractometer Cons:
-A need to calculate *IF* the ambient temp is above 86F or below 50F
-Measuring something very specific (In our case, most refractometers are meant for measuring Brine, not Sea Water, so a small adjustment needs to be made (Shooting for 36.7 ppt of our saltwater instead of 35 ppt due to the difference between brine and natural seawater (Calcium and Magnesium ions affect the refraction).
-Requires constant calibration (though some papers argued this was also a pro due to being able to verify quickly if it was accurate or not)

I tried a cursory search for a few of the articles I had read because I have limited time right now, and the only thing I could find that had a direct comparison of Hydrometer to Refractometer was a paper written by a research team into Glycol coolants. It found that the refractometer in their use case was 6-8 times more accurate than the floating hydrometer due to temperature fluctuations. When I have more time (perhaps over the weekend or later tonight) I will try and search again to find any of the specific articles.

 

[Reef.]

To be clear here, most refractometers these days are ATC (Auto Temperature Compensation) Refractometers, refractometers were also initially created in a lab, and the ATC kind have a typical variability of 10-30 C (Meaning that you won't get inaccuracy until the ambient temperature is below 10C or above 30C (50 F - 86 F). They, too, are often created/calibrated at a specific ambient temperature (in this case, 20C or 68F is most often chosen as the normal/calibrated ambient room temperature).

From my understanding of the articles I've read, which mainly cover in-the-field usage, it weighs out like this:

Cons that lead to inaccuracy:
Hydrometer Cons:
-Affected by micro-bubbles
-Affected by microscopic solids in the solution you're measuring (not dissolved solids (This was in an article about using them to measure sugar concentration in juice from fruits or grapes (winemaking). I am not sure how relevant it is to our hobby, though a copepod or film algae clinging to the outside is certainly analogous to what the article was saying)
-Affected by the temperature of the solution in the cylinder (most of them stated circumvention involves measuring the temperature until it reaches an equilibrium with the ambient temp and then recording both the temperature and the reading and then performing math to get the correct reading)
-Highly Fragile (something about the card in the stem showing the readings, I didn't fully understand it)
-Susceptible to any residue from improper cleaning in both the cylinder and on the hydrometer

ATC Refractometer Cons:
-A need to calculate *IF* the ambient temp is above 86F or below 50F
-Measuring something very specific (In our case, most refractometers are meant for measuring Brine, not Sea Water, so a small adjustment needs to be made (Shooting for 36.7 ppt of our saltwater instead of 35 ppt due to the difference between brine and natural seawater (Calcium and Magnesium ions affect the refraction).
-Requires constant calibration (though some papers argued this was also a pro due to being able to verify quickly if it was accurate or not)

I tried a cursory search for a few of the articles I had read because I have limited time right now, and the only thing I could find that had a direct comparison of Hydrometer to Refractometer was a paper written by a research team into Glycol coolants. It found that the refractometer in their use case was 6-8 times more accurate than the floating hydrometer due to temperature fluctuations. When I have more time (perhaps over the weekend or later tonight) I will try and search again to find any of the specific articles.

Just to add, some refractometers I believe are already adjusted for sea water, the two I use both claim they are designed for sea water not brine.

If in your research you can see why the ATC claims to adjust for room temp and not water temp, but in practice I do not get an accurate reading unless I leave the sample on the prism for 3-4mins, yet the manual claims water temp adjusts to the refractometer in seconds? This was the reason why I was getting incorrect results.

 

[Treefer32]

Solved it, was doing my head in…I wasn’t waiting long enough for the ATC on the refractometer to kick in fully, I would see the 35ppt reading and not bother to wait to see if the reading was still changing.

Never really read of a recommended wait time for the ATC to do it’s thing, how long does everyone wait?

I don't know if refrac's are sent with instructions anymore, but, I remember when I got my ten year old refrac the instructions said to wait 60 seconds for the refrac to adjust to the water temp and the water temp to adjust to room temp. I've always since then counted 60 seconds before looking at the refrac. I had a reefing friend that worked at local fish store (all salt water) and he's said in his working there he had never been told to wait when checking with a refrac. He saw me doing it and wondered what I was doing and why.

Maybe new refracs don't have a wait time. I don't know. I've always done it. ;)

And yes Glass hydrometers are much more accurate than refracs just that you have to calculate the temperature difference. My refrac is off by .015 (I can't calibrate it because the screw doesn't go high enough to calibrate it).

I probably need a new refrac. But point being, I test at least once a year with a glass hydrometer to make sure my refrac hasn't gone further off than it is.

 

[JNalley]

Just to add, some refractometers I believe are already adjusted for sea water, the two I use both claim they are designed for sea water not brine.

Yes, there are some calibrated for seawater, but then recalibrating with brine throws this off. Most of the seawater ones I am aware of calibrate with RODI and only read 0-40 ppt instead of 0-100, though I'm sure some out there go 0-100...

If in your research you can see why the ATC claims to adjust for room temp and not water temp, but in practice I do not get an accurate reading unless I leave the sample on the prism for 3-4mins, yet the manual claims water temp adjusts to the refractometer in seconds? This was the reason why I was getting incorrect results.

The copper armature in the body adjusts the prism based on ambient temp, you still need the water to reach ambient temp to be accurate. Though it shouldn't take 3-4 minutes for a couple of drops to reach ambient temp, it should normally be about 30 seconds to a minute, though does depend on the volume of water and the temperature differential between the water and the ambient temp, and most refractometers tell you to wait. What may be happening is the wait for the refractometer to reach room temp. If it's stored in an insulated box, it's at least possible the temperature inside the box and the room differ by a degree or two causing the delay... But I couldn't tell you really.

 

[TangerineSpeedo]

To be clear here, most refractometers these days are ATC (Auto Temperature Compensation) Refractometers, refractometers were also initially created in a lab, and the ATC kind have a typical variability of 10-30 C (Meaning that you won't get inaccuracy until the ambient temperature is below 10C or above 30C (50 F - 86 F). They, too, are often created/calibrated at a specific ambient temperature (in this case, 20C or 68F is most often chosen as the normal/calibrated ambient room temperature).

From my understanding of the articles I've read, which mainly cover in-the-field usage, it weighs out like this:

Cons that lead to inaccuracy:
Hydrometer Cons:
-Affected by micro-bubbles
-Affected by microscopic solids in the solution you're measuring (not dissolved solids (This was in an article about using them to measure sugar concentration in juice from fruits or grapes (winemaking). I am not sure how relevant it is to our hobby, though a copepod or film algae clinging to the outside is certainly analogous to what the article was saying)
-Affected by the temperature of the solution in the cylinder (most of them stated circumvention involves measuring the temperature until it reaches an equilibrium with the ambient temp and then recording both the temperature and the reading and then performing math to get the correct reading)
-Highly Fragile (something about the card in the stem showing the readings, I didn't fully understand it)
-Susceptible to any residue from improper cleaning in both the cylinder and on the hydrometer

ATC Refractometer Cons:
-A need to calculate *IF* the ambient temp is above 86F or below 50F
-Measuring something very specific (In our case, most refractometers are meant for measuring Brine, not Sea Water, so a small adjustment needs to be made (Shooting for 36.7 ppt of our saltwater instead of 35 ppt due to the difference between brine and natural seawater (Calcium and Magnesium ions affect the refraction).
-Requires constant calibration (though some papers argued this was also a pro due to being able to verify quickly if it was accurate or not)

I tried a cursory search for a few of the articles I had read because I have limited time right now, and the only thing I could find that had a direct comparison of Hydrometer to Refractometer was a paper written by a research team into Glycol coolants. It found that the refractometer in their use case was 6-8 times more accurate than the floating hydrometer due to temperature fluctuations. When I have more time (perhaps over the weekend or later tonight) I will try and search again to find any of the specific articles.

Thanks for that. For me a Hydrometer is my most accurate means, for I only need to control the temperature to get a proper reading. In fact it is the only way I can get a proper reading when I mix salt because I use TM Bio-Actif salt mix. It will read low if you are using a hanna. I believe that the hand held Refractometer’s do not have a ambient temp tolerance as wide of a spectrum as you stated, or at least the $30 ones I have. I thought I had a golden one that would read accurately at distilled and 35ppt NSW reference. Then it got cool in the house. ( we always have the California climate control our indoor climate)
Honestly, salinity testing drives me nuts! I have every method and tool and None of them will read the same as each other I have two handheld refractometers, a Milwaukee electronic reflectometer, a hanna EC meter, the TM Hydrometer, I guess you can include my Apex one as well. The two things that I know are a constant are; my TM hydrometer and the ocean a block away from me. (non- rain)

 

[Liftoff]

Try to calibrate your devices to know liquids (no salinity; add some salinity etc.). In this way you get more points to derive your calibration from.

Also, the temperature at which the refractometer is at/stored will be the dominating temperature for the calibration/measurement, not the water temperature at the time.

 

[JNalley]

Thanks for that. For me a Hydrometer is my most accurate means, for I only need to control the temperature to get a proper reading. In fact it is the only way I can get a proper reading when I mix salt because I use TM Bio-Actif salt mix. It will read low if you are using a hanna. I believe that the hand held Refractometer’s do not have a ambient temp tolerance as wide of a spectrum as you stated, or at least the $30 ones I have. I thought I had a golden one that would read accurately at distilled and 35ppt NSW reference. Then it got cool in the house. ( we always have the California climate control our indoor climate)
Honestly, salinity testing drives me nuts! I have every method and tool and None of them will read the same as each other I have two handheld refractometers, a Milwaukee electronic reflectometer, a hanna EC meter, the TM Hydrometer, I guess you can include my Apex one as well. The two things that I know are a constant are; my TM hydrometer and the ocean a block away from me. (non- rain)

No problem. I am working on a 25-30 page paper for school and it's kicking my backside right now, which is why I can't look up more. Can I ask though, what does the salt mix have to do with it? Is there something different about the Bio-Actif salt? I've used their Pro salt, but never any of the others.

With hand-held refractometers, it really is a "get what you pay for" sort of scenario since a ton of the cheaper ones are just mass-produced junk, they'll get the job done in a pinch, but you're better off going for a known lab-grade one. Vee Gee Scientific and a few others make some high-quality ones that labs (hydrogeology and other industries) use worldwide. Lab-grade usually start in the low $100's and can go up as high as $300+. Red Sea makes a Seawater refractometer for ~$70 (RedSea Refractometer), but some of the wording in their description doesn't line up with what the scientific communities say about their refracts, so it could just be marketing nonsense.

Most refractometers will tell you on the screen what temperature they're calibrated for (typically signified by a 20/20 or something similar (Ambient temp of 20C/Water temp of 20C)) on the scale, and most ATC refractometers tell you what variance the ATC has (typically 10C - 20 or 30C). Though, as I said, the cheap ones are cheap and may not be accurate in this area.

The one thing I think needs to be fully understood is that different refractometers are task-specific, as I said before, most of the Salinity refractometers are calibrated for Brine and putting Seawater in them throws off the reading by as much as 1.7 ppt or something along those lines. Buying one that specifically reads SeaWater is the best bet (The Vee Gee one I linked above is calibrated for Sea Water). They all also have different ways of calibrating, some of them (Seawater ones) calibrate with Distilled/RODI, while some (Brine typically) calibrate using 35ppt solution, following the calibration method from the manufacturer is the best route to go, and when testing accuracy using a solution, it's helpful to know if that solution is Brine or if it's Sea Water. 35ppt Brine should read as 33.3ppt on a Seawater refractometer (I think), but will read as 35ppt on a Saltwater/Brine Refractometer. The unfortunate thing we run into within the hobby is that "saltwater" is often our colloquial term for seawater, and some "saltwater" refractometers are only measuring Brine, not Seawater/Saltwater as we know it.

 

[TangerineSpeedo]

No problem. I am working on a 25-30 page paper for school and it's kicking my backside right now, which is why I can't look up more. Can I ask though, what does the salt mix have to do with it? Is there something different about the Bio-Actif salt? I've used their Pro salt, but never any of the others.

With hand-held refractometers, it really is a "get what you pay for" sort of scenario since a ton of the cheaper ones are just mass-produced junk, they'll get the job done in a pinch, but you're better off going for a known lab-grade one. Vee Gee Scientific and a few others make some high-quality ones that labs (hydrogeology and other industries) use worldwide. Lab-grade usually start in the low $100's and can go up as high as $300+. Red Sea makes a Seawater refractometer for ~$70 (RedSea Refractometer), but some of the wording in their description doesn't line up with what the scientific communities say about their refracts, so it could just be marketing nonsense.

Most refractometers will tell you on the screen what temperature they're calibrated for (typically signified by a 20/20 or something similar (Ambient temp of 20C/Water temp of 20C)) on the scale, and most ATC refractometers tell you what variance the ATC has (typically 10C - 20 or 30C). Though, as I said, the cheap ones are cheap and may not be accurate in this area.

The one thing I think needs to be fully understood is that different refractometers are task-specific, as I said before, most of the Salinity refractometers are calibrated for Brine and putting Seawater in them throws off the reading by as much as 1.7 ppt or something along those lines. Buying one that specifically reads SeaWater is the best bet (The Vee Gee one I linked above is calibrated for Sea Water). They all also have different ways of calibrating, some of them (Seawater ones) calibrate with Distilled/RODI, while some (Brine typically) calibrate using 35ppt solution, following the calibration method from the manufacturer is the best route to go, and when testing accuracy using a solution, it's helpful to know if that solution is Brine or if it's Sea Water. 35ppt Brine should read as 33.3ppt on a Seawater refractometer (I think), but will read as 35ppt on a Saltwater/Brine Refractometer. The unfortunate thing we run into within the hobby is that "saltwater" is often our colloquial term for seawater, and some "saltwater" refractometers are only measuring Brine, not Seawater/Saltwater as we know it.

TM Bio-Actif salt is their Pro Reef with their Actif Bacteria added to it. Because it becomes an organic mixture when you mix it an EC meter (Hanna) will read low) I probably should get a VeeGee, but to be honest I use my EC meter for spot checks and my critical mixing I use the TM anyway.